Protesters in London, Madrid, Milan Say the Apps Skirt Regulations

LONDON—Thousands of European taxi drivers snarled traffic in cities across the continent, protesting car-hailing services provided by Uber Technologies Inc. and others.

Drivers in London, Paris, Berlin and Madrid, among others, have complained that the services aren't competing on a level playing field. In some cities, Uber allows users to hail a privately licensed taxi through a smartphone app or organize a car share, often...